Lake Tana''s water balance is not well understood since a large part of the Lake Tana basin is ungauged with uncertain inflows. In recent studies by Kebede et al. (2006) and SMEC (2007) closure of Lake Tana water balance is obtained by runoff from ungauged catchments that cover a large part of the Lake Tana basin. In this thesis water balance terms are calculated on a daily base while simulated daily lake levels are compared to observed levels for the period 1995 to 2001. Daily flows from an ungauged catchment are estimated by transferring model parameters from gauged catchments using a regionalisation procedure, a spatial proximity procedure and catchment area ratio''s methods. In regionalisation gauged catchment model parameters of the conceptual rainfall-runoff model HBV are transferred to ungauged catchments based on catchment characteristics to allow for runoff simulation. In the proximity procedure model parameters of gauged catchments are transferred to neighbouring ungauged catchment. In area ratio model parameter sets of gauged catchments are transferred to ungauged catchments of comparable area.